Process for the radiation curing of unsaturated polyester resins in the presence of sulfur-vulcanized elastomer

ABSTRACT

This invention relates to a method of curing unsaturated polyester resins in contact with elastomers by polymerization employing ionizing radiation. This invention, which overcomes all drawbacks in the prior art whereby unsaturated polyester resins under the afore-mentioned condition could not be cured, only remaining in gel form, can be widely used for various kinds of fiber glass reinforced plastics and coated goods including decorative laminates and the like.

United States Patent [1 1 Gotoh et a1. 1 I

[451 Nov. 20, 1973 [75] Inventors: Kazuo Gotoh; Kunio Araki; TakashiSasaki, all of Takasaki, Japan [73] Assignee: Japan Atomic EnergyResearch Institute, Tokyo, Japan 22 Filed: June 15, 1971 21 App1.No.:153,397

[30] Foreign Application Priority Data June 18, 1970 Japan 45/53095 [52]US. Cl 204/l59.l9, 117/93.31, 117/148, 156/272, 204/159.14, 204/159.15,

[51] Int. Cl. B0lj l/10, C08d 1/00, C08f1/16 [58] Field of Search204/159.14, 159.15; 264/25, 26; 117/93.31, 139

[56] References Cited UNITED STATES PATENTS 3,247,012 4/1966 Burlant117/139 3,661,614 5/1972 Bassemir et al 204/159.23

Primary ExaminerMurray Tillman Assistant ExaminerRichard B. TurerAttorney-David Toren et al.

[57] ABSTRACT This invention relates to a method of curing unsaturatedpolyester resins in contact with elastomers by polymerization employingionizing radiation.

This invention, which overcomes all drawbacks in the prior art wherebyunsaturated polyester resins under the afore-mentioned condition couldnot be cured, only remaining in gel form, can be widely used for variouskinds of fiber glass reinforced plastics and coated goods includingdecorative laminates and the like.

6 Claims, No Drawings PROCESS FOR THE RADIATION CURING OF UNSATURATEDPOLYESTER RESINS IN THE PRESENCE OF SULFUR-VULCANIZED ELASTOMERBACKGROUND OF THE l NVENTlON This invention relates to a method ofcuring unsatu rated polyester resins, in particular unsaturatedpolyester resins in direct contact with a surface film or molding ofsulfur vulcanized natural or synthetic rubber.

The unsaturated polyester resins are being used very commonly andextensively as resins for FRP (fiberglass reinforced plastics),decorative laminates, and coatings, and a number of methods of curingthese resins are already known. In general, methods are being used forcuring by heating in the presence of a catalyst added as apolymerization initiator or curing after a certain induction time atambient temperture with the additional use of polymerizationaccelerators.

However, it is known that processeswherein FRP molding materials usingan unsaturated polyester resin are pressed against vulcanized rubber asin the pressure bag, the vacuum bag, the autoclave or the plungermolding method (Ref. Modern Plastics Encyclopedia Vol. 40, No. lA, page666, September 1962), those wherein the molding materials or unsaturatedpolyester resin coatings are cured over a vulcanized rubber bag orsheet, and those in which the afore-mentioned molding materials orunsaturated polyester resin coated or impregnated materials are curedcovered with a vulcanized rubber tube, bag or spirally wound narrowbeltlike sheet are invariably accompanied by a shortcoming in that ifthe unsaturated polyester resin is placed in direct contact with thenatural or synthetic rubber vulcanized with sulfur, the portion of theunsaturated polyester resin at the contact area remains in a viscousliquid or a tacky gel form even when the remaining portion has beenpolymerized and cured.

The reasons for the occurrence of this phenomenon are considered to be(l) thata chain transfer reaction or inhibtion reaction which takesplace due to the disulfide linkage -S-S-- bond), mercaptan or some othersubstance in the vulcanized rubber coming in contact with monomers inthe resin inhibits the curing reaction of the resin whichinvo lvespolymerization as a main object and (2) that the curing reaction of theresin is virtually checked by the degradative chain transfer reaction inwhich allyl type (Cl-lCl-l= radicals ar fa med. a @FPS cfhvq af genatoms adjacent to the double bonds being dis- For this reason, whenpreviously FRP goods were manufactured using unsaturated polyesterresins or when these resins were applied as coatings, it has been usualeither that no elastomers are used for the molding sheet or basematerial, or that if an elastomer must be used, special care is taken asit is necessary to insert an inert material which does not interferewith the curing of the resins, such as polyvinyl alcohol films andparaffin, at the boundary of contact between the elastomer and resin.However, the latter method has the disadvantage that there is apossiblity of causing cracks or wrinkles to the inert material when theelastomer is expanded over intricately irregular surfaces and thusbringing about increased cost.

Furthermore, when unsaturated polyester resins are cured with paraffinwhich is used so as to' keep the resin out of direct contact with theelastomer in the presence of a thermally decomposed type of catalystwhich liberates heat, it is often the case that rejects arise among theproducts due to the paraffin fusing into the unsaturated polyesterresin.

Moreover, in processing unsaturated polyester resins by the matched-diemolding method, a method might be used which is so designed as to adjustthe pressure between themold, male or female, and the laminate layer tomake the thicknesses of the ultimately molded objects uniform. This isdone by placing the molding material which is pre-impregnated with anunsaturated resin in the mold, male or female, and further placing overit an elastic layer which is only minimally subject to cold flow becauseof its ease of expansion or contraction. A vulcanized rubber productcapable of expansion and contraction was used in the various types ofmold frames for this purpose, very desirable results might be expectedwith regard to the rate of cure, aging, and product properties since thestrains caused by the contraction of its volume which takes place whenthe resin cured, would be absorbed by the rubber layer so that nospecial techniques might be required in the operation of the press.However, for the reasons described hereinabove, matched-die molding ofunsaturated polyester resins which could use an elastomer have beenemployed because of the foregoing described limitations.

STATEMENT OF THE INVENTION The first object of this invention is toremedy the drawbacks which have heretofore existed as described in theforegoing and provide a novel and improved and more facile method ofcuring unsaturated polyester resins. The second object of this inventionis to produce unsaturated polyester resin FRP goods using an elastomeras a mold or base.

The present invention consists of a method of curing which'comprisessubjecting the unsaturated polyester resins to ionizing radiation. Theinventors have ascertained, after having studied various methods ofcuring unsaturated polyester resins in contact with elastomers, that itis possible to completely cure unsaturated polyester resins, notexcepting the portions thereof in contact with sulfur vulcanizedelastomers, by using ionizing radiation without resorting to any of themethods known in the prior art.

The unsaturated polyester resins described as the subject matter of thisinvention may be any of those already known. In particular, reactionproducts of unsaturated dibasic acids or acid anhydrides, such as,maleic acid or maleic anhydride, fumaric acid, itaconic acid or itaconicanhydride and citraconic acid or citraconic anhydride, and dihydric orother polyhydric alcohols, or partly modifying the aforementioned acidswith aliphatic, aromatic or alicyclic carboxylic acids having acarboxylic group or their halogen derivatives, and the solutionsobtained by dissolving them in one or more types of polymerizablemonomers, such as styrene, vinyl acetate, vinyl toluene, chlorostyrene,divinylbenzene, methacrylates, acrylates, acrylonitrile,methacrylonitrile, diacrylphthalate, triacrylcyanurate, and so forth areconsidered suitable. (Ref. S. OLEESKY, G.

MOHR, Handbook of Reinforced Plastics 1964) Various kinds of pigments,dyes and fillers may also be added to them.

These unsaturated polyesters in general are 1,000 4,000 in molecularweight. Since resins have many sorts of different properties dependenton the combination and amounts of unsaturated acids, saturated acids, orglycols, used as the main constituents, and the monomers serving assolvents, of which there are a great number of varieties, they should beused selectively,-

taking into account their properties and performance which aredistinctively suited for specific applications.

The ionizing radiation applicable in accordance with this invention isionizing radiation or accelerated particle radiation from any source,exemplified by ,B -rays, 'y-rays, an accelerated electron beam, X-rays,neutron beam and so forth.

The dose rates of the ionizing radiation in 'accordance with thisinvention are 10 l rad/hr. and more desirably 5 X 10 rad/hr., and thecuring temperatures are -40- +1 C and, more desirably, in the range of0- 50C. The processing pressure may be around atmospheric, but it shouldnecessarily be maintained at 0.5 2 kg/cm G when the pressure bag orautoclave process is used and at 100 700 mmHg in the case of the vacuumbag process. Nevertheless, in any case, the processing temperatures andpressures may be the same as those used when all the respectiveunsaturated polyester resins so far known are cured. The dose rate maysuitably be determined dependent on the type of resin, its amount, thehardness required of the end product, the curing time used and so forth.

The elastomers may be a sulfur-vulcanized rubber selected optionallyfrom natural rubber, butadienestyrene rubber, butyl rubber, nitrilerubber, chloroprene rubber, polybutadiene rubber, isoprene rubber,ethylene-propylene terpolymer and the like.

According to this invention it is possible to easily yet completely cureunsaturated polyester resins in contact with an elastomer without'any ofthe difficulties previously encountered. Consequently, there is derivedThe advantages offered by this invention will be further,

described hereinbelow.

l. Hollow objects can be obtained by lamination by coating unsaturatedpolyester resin molding materials canized rubber, curing the resin byapplying ionizing radiation and subsequently removing the hollow bodyafter contracting it. v

2. Molded goods resembling molded objects madeby the matched-die moldingprocess can be obtained by pouring molding materials similar to thoseaforementioned into female molds made of metal, plastics, gypsum,concrete, wood or the like, and then introducing compressed air into abag of vulcanized rubber placed over them, curing the molding materialsby subjecting them to ionizing radiation while they are being pressed bythe rubber bag against the mold and subsequently removing the rubber.bag after contracting same.

3. Molded goods resembling those made by the matched-die molding methodcan be obtained by depositing molding materials on male molds made ofany of the same materials mentioned in the foregoing, covering theirupper side or periphery with vulcanized rubber, curing the moldingmaterials by ionizing radiation applied while keeping the space betweenthe rubber bag or rubber and the mold under vacuum and applyingatmospheric pressure (external pressure) to the molding materials, andsubsequently removing the rubber.

4. After placing plywood panels, metal plates, wood pieces coated orimpregnated with an unsaturated polyester resin or other impregnated orcoated materials on a conveyor belt made of vulcanized rubber, the resinis cured by applying ionizing radiation, impregnated or coated objectswhich are cured flatly and smoothly at the areas in contact with therubber can be obtained.

5. Molded objects having a beautiful surface and appearance can beobtained successively or intermittently by curing unsaturated polyesterresin coated or impregnated articles in shape of rod, hollow body orprofile form, which are coveredby a vulcanized rubber tube, bag orspirally wound belt, or molding materials by applying ionizing radiationsuccessively o'r intermittently and removing the rubber cover.

6. Since the vulcanized rubber contracts simultaneously with thecontraction of the cured unsaturated polyester resins, a flat, smoothsurface can be obtained.

7. Dimensionally accurate molded objects can be obtained by curingunsaturated polyester resins while expanding a rubber belt in a lateraldirection.

.8. Dimensionally accurate and V-shaped objects can be obtained, forexample, by changing the rubber belt into a V-shape in a semi-curedcondition and subsequently curing them completely. In contrast, ifparaffin or the like is used between the vulcanized rubber andunsaturated polyester resin as the aforesaid process, desired objectscannot be obtained due to both materials losing adhesion or uncuredareas arising due to cracks in the paraffin, for example.

Typical examples of the method of the present invention will begiven'hereinafter but should not be construed as limiting the scope ofthis invention. All the parts indicated in the Examples represent partsby weight.

"EXAMPL 1] A commercial unsaturated polyesterresinwhi'ch consists ofpoly(propylene maleate phthalate) with an addition of styrene atapproximately 33 percent of.the total amount of the former was appliedin a thickness of approximately lmm directly on to a 1mm thick sulfurvulcanizednatural rubber sheetcontaining carbon black. The other side ofthe resin was covered with cellophane to shut it off from the air. When10 M rad electron beam was subsequently applied at lmA, at atmosphericpressure and ambient temperature, the resin was cured rapidly, easilyand completely. Moreover, the cured resin could be released cleanly fromthe surfaces of both the cellophane and rubber. The surface hardness ofboth sides as measured by the Barcol tester reached 90.

in comparison, in the case of a method in which 1.0 part of methyl ethylketone peroxide and 0.5 part of cobalt naphthenate were added as acatalyst and a cocatalyst respectively to the above-mentionedunsaturated polyester resin, which was covered with cellophane on theupperside, while the underside being in direct contact with the sulfurvulcanized natural rubber, the one side of resin covered with thecellophane was completely cured after the lapse of two hours at ambienttemperature but even after subsequently heated for additional two hoursat 100C, the side in contact with the rubber was not cured, remaining ina viscous liquid form.

EXAMPLE 2 An approximately 1mm thick fiber glass reinforced plasticssheet molding material pre-impregnated with a commercial unsaturatedpolyester resin which is composed of poly(diethylene glycol maleateisophthalate) with approximately 30 percent ofstyrene and 3 percent ofmethyl methacrylate added was placed in a female mold made of gypsum.The molding material, pressed against the mold with a 0.5mm thicksulfur-vulcanized SBR pressure bag into which 2 kg/cm G compressed airwas passed, was cured after 10 hours irradiation with 60 y-rays at adose rate of 10 rad/hr. Subsequently the rubber bag was removed and agood quality FRP molded article was obtained.

EXAMPLE 3 A plywood panel with a wood pattern printed sheet overlaid wascoated, at a thickness of 200p, with an unsaturated polyester resinconsisting of poly(ethylene propylene fumarate tetrachlorophthalate) towhich approximately 20 percent of styrene and approximately percent ofvinyl acetate monomers were added, and was placed so as to have itsresin coated surface contact with a 0.5mm thick sulfur vulcanized NBR(nitrile rubber) conveyor. Radiation was then applied through the rubberconveyor using a 1 MeV electron beam accelerator at a dose rate of 8 X10 rad/sec. for 2 seconds. After removal form the rubber surface, amatted decorative panel having a high surface hardness was obtained.

EXAMPLE 4 A molding material consisting of 100 parts of an unsaturatedpolyester resin comprised of poly(propylene glyceryl fumarate adipate)to which approximately 20 percent of styrene, approximately 10 percentof methyl methacrylate and approximately 3 percent of acrylonitrile wereadded, combined with parts of chopped glass fiber and 30 parts of silicapowder, was poured into a female mold made of sulfur vulcanizedethylenepropylene terpolymer rubber. The resin was cured by subjectingit to 30 hours irradiation using a 137 'y-ray source at a dose rate of10 rad/hr. When it was subsequently removed from the rubber mold, alarge cast molded object having a beautiful surface free from cracks wasobtained.

EXAMPLE 5 A 1mm thick fiber glass reinforced plastics molding materialimpregnated with an unsaturated polyester resin composed ofpoly(propylene maleate phthalatehexachloro-endomethylene-tetrahydrophthalate) to which approximately 30percent of styrene and 5 percent of methyl methacrylate were added tomake it into a liquid form, was placed between two sheets of sulfurvulcanized polybutadiene rubber. After the resin had been half curedwith one seconds irradiation using a 2 MeV electron beam accelerator ata dose rate of 8 X 10 rad/sec., this semi-cured material, insertedbetween the rubber sheets and shaped into a corrugated pattern, wascured by applying a further irradiation at the same dose rate for 7seconds. When the rubber sheets were removed, a FRP corrugated panelhaving a glossy surface was obtained.

What is claimed is:

1. In a method of curing an unsaturated polyester resin obtained asreaction product of unsaturated acids selected from the group consistingof maleic, fumaric and itaconic acids or citraconic anhydrides withdihydric or polyhydric alcohols and derivatives thereof, wherein saidpolyester resin has a molecular weight in the range of 1,000 4,000 andis in direct contact with an elastomer selected from the groupconsisting of butadiene-styrene rubber, butyl rubber, nitrile rubber,chloroprene rubber, polybutadiene rubber, isoprene rubber, andethylene-propylene terpolymer, said elastomer having been vulcanizedwith sulfur, the improvement which comprises irradiating saidunsaturated polyester resin with ionizing radiation at a dose rate of 1010' rad. per hour at atemperature of from 40- 120C.

2. The method, as claimed in claim 1 wherein the dose rate of ionizingradiation is in the range of from 10 10 rad. per hour.

3. The method as claimed in claim 1 wherein said temperature is in therange of 0- 50C.

4. A method according to claim 1 wherein said ionizing radiation isselected from the group consisting of ,B-rays, 'y-rays, acceleratedelectron beam, X-rays and neutron beam.

5. A method according to claim 1 wherein the processing pressure iswithin the range of 0 2 kg/cm G.

6. A method according to claim 1 wherein the processing pressure iswithin the range of 700 mmHg.

2. The method, as claimed in claim 1, wherein the dose rate of ionizingradiation is in the range of from 105 - 1010 rad. per hour.
 3. Themethod as claimed in claim 1 wherein said temperature is in the range of0*- 50*C.
 4. A method according to claim 1 wherein said ionizingradiation is selected from the group consisting of Beta -rays, gamma-rays, accelerated electron beam, X-rays and neutron beam.
 5. A methodaccording to claim 1 wherein the processing pressure is within the rangeof 0 - 2 kg/cm2G.
 6. A method according to claim 1 wherein theprocessing pressure is wIthin the range of 100 - 700 mmHg.